Ronnie's girlfriend, Jen Harley, gave birth to a baby girl on Tuesday, according to E! News.
"He's over the moon," a source told the website of the new father.
Fans speculated Jen might be in labor when Ronnie missed the London premiere of Jersey Shore: Family Vacation, which premieres April 5 at 8PM ET/PT on MTV.
Jen also documented her visit to the hospital Monday on Instagram Stories, explaining, "Ron lands at seven so we have five hours [until then]. I'm feeling very very uncomfortable." Jen was accompanied by her best friends at the time, and everything reportedly turned out to be fine.
Ronnie and Jen announced they were expecting their first child together in December 2017, and one month later, they celebrated news of a baby girl being on the way at a gender-reveal party.
When Ronnie shared photos of the event, he captioned them with the following hilarious hashtags: "#WaitWhat #Huh #DUHHH #AMillionThingsWentThroughMyHead #FirstThoughtWasOkNowIDefNeedAGun #JesusHowMuchIsTheWeddingToCostMe #DoIHomeSchoolOrNotHomeSchool #AllGirlCatholicHighSchool #NoCellPhoneUntilShesMarried #ThisIsWhyIWaited32Yrs."
Jen -- who is already mom to an 11-year-old son from a previous relationship -- later enjoyed a floral-themed baby shower in Las Vegas in March.
"We are so thankful to have such good friends and family to come support us and fly in from all over the country!" Jen shared on Instagram at the time, standing behind a table filled with pink cupcakes and sweets.
"Special thanks to... my BFF for planning this for 4 months... That was so much fun. we have the most amazing pics!"
Ronnie began dating Jen last year after he split from Khloe Kardashian's best friend Malika Haqq, whom he met on Season 2 of Famously Single. Ronnie and Malika called it quits on their romance in February 2017.